1. Field of the Invention
The present invention relates to methods for making flowable, highly concentrated powders and tablets of hygroscopic plant growth regulator compounds, and more specifically to processes to dry mepiquat chloride aqueous solutions to form flowable highly concentrated solid products.
2. Background of the Prior Art
Plant growth regulators affect the physiology of plant growth and influence the natural rhythm of a plant. More specifically, plant growth regulators may, for example, reduce plant height, stimulate seed germination, induce flowering, promote or inhibit fog, darken leaf coloring, minimize lodging of cereals, slow grass growth on lawns, reduce boll rot and provide better boll retention in cotton.
Plant growth regulators may be applied to plants in a variety of methods including different formulations. Of these various methods, use of liquid and dry compositions are the most common. The particular formulation desired and resulting efficacy enhancement will greatly depend upon the species to be treated, environmental conditions, the geographical area and the climatology of the area at the time of treatment.
The plant growth regulator, known trivially as mepiquat chloride, is generally used to control various aspects of cotton boll growth. See, for example, Khafaga, Angew. Botanik 57, 257-265 (1983); Sawan et al., J. Agronomy & Plant Science, 154, 120-128 (1985); U.S. Pat. Nos. 3,905,798 and 4,447,255.
Mepiquat chloride is used as a plant growth regulator in agriculture. Mepiquat chloride has a high water solubility of more than 600 g/L. The melting point is 223.degree. C. The substance is very hygroscopic, readily absorbing moisture from humid air, so much so, that the dry powder can turn to liquid when exposed to ambient humid air. During Storage,.the solid mepiquat chloride readily cakes and sticks container surfaces, even at low residual water contents of less than 0.5%.
These properties make it extremely difficult to dry mepiquat chloride. In conventional spray dryers, the material is very difficult to dry. It must be atomized extremely finely to reduce the moisture to a suitable level and even then it retains too much water to dry practically. The product remains sticky and adheres to the walls of the dryer and the dryer ducts and cyclones, eventually plugging the ducts and cyclones. Furthermore, powder from such a process, because it is so fine, flows poorly out of the dryer, and upon storage in a drum, is rendered unflowable due to caking.
Solid forms of plant growth regulators offer a number of key advantages, including convenience, increased stability and shelf life, as well as reduced packaging, storage and shipping costs. Additionally, there is the possibility of future government regulation requiring solid forms of agricultural products in order to reduce handling of contaminated packaging of these products during field application and during disposal. These dry flowable plant growth regulating compounds would be safer for the farmer to use and dispose of, and also result in a smaller volume of hazardous waste being produced.
There is a need for dry, flowable, highly concentrated powder and tablet formulations of hygroscopic plant growth regulators.